Liquid injection type screw compressor

ABSTRACT

A liquid injection type screw compressor in which, in a compression stroke of an working space formed by male and female rotors, liquids such as oil or water is prevented from leaking from the high pressure working space to a gas inlet side, suction resistance of gas sucked from the gas inlet to a rotor casing is reduced to improve volumetric efficiency, and shape forming of the casing is simplified. 
     The liquid injection screw compressor has the male and female rotor pair of screw rotors, the rotor casing ( 1   a   , 1   b ) having a bore for receiving the rotors, a gas suction opening and a gas outlet that are provided in both end sections of the casing and communicate with the bore, and a lip section ( 4 ) projected from a bore surface ( 2 ) positioned more on the upstream side than a suction seal line ( 5 ) of the casing in order to prevent a back flow of the liquid from the bore surface toward the gas inlet side. The lip section ( 4 ) is positioned in a region surrounded by the suction seal line ( 5 ) and a line separated by a distance of one screw pitch of the rotors from the suction closure line ( 5 ) to the suction opening side.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid injection type screwcompressor comprising a pair of male and female screw rotors that areinstalled in a space surrounded by a bore face within a casing of thecompressor, while a liquid such as oil or water is injected to the boreface; whereby, a lip part is provided so as to prevent the liquid fromflowing-back to a working gas inlet side, being placed on the bore face,within a range from a suction seal line (a suction closure line or asuction containment boundary locus) to a line parallel thereto apartfrom the suction seal line, by a distance equal to one screw pitch (atooth groove distance in the rotor axis direction) of the rotors.

In hitherto known liquid injection type screw compressors, a pair of amale screw rotor and a female screw rotor within a casing of thecompressor are engaged in each other, so as to form a working/operationspace inside which a liquid such as oil or water is injected whereby aworking substance of a gas-liquid mixing phase is pressurized. Theliquid injection brings the screw compressor a cooling function, asealing function, and a lubricating function; thus, the compressor ofthe type obtains high efficiency even during a low speed operation,becoming widespread in the industry.

The bore faces forming the working space within the casing of thecompressor are important elements so as to secure gas/liquid tightness,when the working space is under a compression process where a gas sealacross adjacent tooth spaces is required; consequently, it is aprerequisite to keep the clearance between the addendum circles of therotors (tooth tip surfaces of the rotors) and the bore faces as small aspossible. In this specification, the bore faces in the part as mentionedare called main bore faces.

On the other hand, a gas leakage between adjacent tooth spaces does noteffect on the performance of the compressor when working spaces areunder gas suction process; therefore, the bore faces in the associatedpart as mentioned are expanded toward outside in comparison with themain bore faces so that a power consumption is reduced by evadinguseless possible friction between the bore faces and the tooth tips;thus, the bore faces in the part as mentioned are called expanded borefaces.

In conventional liquid injection type screw compressors as describedabove, a weir (a lip part) is provided therein so as to prevent oil fromscattering through a suction side end face of the rotor casing toward agas inlet side; thus, it is intended to preserve the compressorvolumetric efficiency and reduce the compressor power loss.

Conventional screw compressors with such a weir as mentioned aredisclosed, for instance, in a patent literature 1 (JP patent:1967-10027), a patent literature 2 (JP: 1991-194183) and a patentliterature 3 (JP: 1999-13661).

The FIGS. 1 and 2 in the patent literature 1 disclose that a lip (weir)44 is provided between a gas inlet 24 and an expanded bore part 40 so asto lessen a heat exchange between a hot back-flow gas from a compressionspace formed in a rotor tooth space, and a flow-in gas from the gasinlet 24.

On the other hand, the FIG. 1 in the patent literature 2 discloses a lip(weir) 39 that is provided at a suction side end-face of a casing 3 sothat the lip 39 prevents a back-flow oil from flowing from expanded boreparts 7 and 8 back to a gas inlet side, from warming-up an inhaled gas,and also from deteriorating a charging efficiency of the inhaled gas tobe charged into a rotor teeth space.

Moreover, the patent literature 3 discloses that the oil injected into aworking space flows back to a gas inhaling space; thereby, an oil mistgenerated from the back-flow oil suspends in the gas inhaling space,while the oil mist heats up the inhaled gas under a suction process;namely, a phenomenon, what is called inhaled gas heating, occurs; thus,the phenomenon increases a temperature of the gas to be compressed aswell as expands a volume thereof; as a result, in a displacement typecompressor that needs to inhale a gas of a constant specific volume, notonly a reduction of mass-throughput but also a deterioration ofvolumetric efficiency are brought.

In order to evade the above-mentioned difficulties, according to thepatent literature 3, as shown in FIG. 2 of the patent literature 3 a lippart 5 is provided at a suction side end-face of a casing 3 thataccommodates the rotors, so that the lip part 5 protrudes inside, i.e.toward screw rotors; further, a heat-up prevention wall (a baffle plate)8 to close a gap between the screw rotors and the lip part 5 is providedso as to prevent an inhaled gas from leaking toward a gas inlet side.

FIGS. 9 a and 9 b that are attached to this application shows a casingfor conventional screw rotors; for explanatory convenience, FIG. 9 ashows a divided upper half and FIG. 9 b shows a divided lower half. InFIGS. 9 a and 9 b, a space that accommodates a male rotor and a femalerotor is formed inside the casing 01; thereby, the boundary of the spacecomprises:

-   -   a male rotor side main-bore-face 02 a that faces a male rotor        tooth tip with a slight clearance A1,    -   a female rotor side main-bore-face 02 b that faces a female        rotor tooth tip with a slight clearance A2,    -   a male rotor side expanded-bore-face 03 a that faces a male        rotor tooth space during a gas suction process, and a male rotor        tooth tip with a clearance B1 greater than the mentioned        clearance A1, and    -   a female rotor side expanded-bore-face 03 b that faces a female        rotor tooth space during a gas suction process, and a female        rotor tooth tip with a clearance B2 greater than the mentioned        clearance A2.

Further, a lip part 04 is provided along a suction side end-face of acasing 01 so that the lip part 04 of the casing 01 protrudes inside,toward screw rotors; on the other hand, a suction seal line (a suctioncontainment boundary locus) 05 is formed on a boundary between the malerotor side main-bore-face 02 a and the male rotor sideexpanded-bore-face 03 a as well as between the female rotor sidemain-bore-face 02 b and the female rotor side expanded-bore-face 03 b.

In the configuration as stated above, a working space is formed with atooth space of the male rotor and another working space is formed with atooth space of the female rotor, the pair of tooth spaces beingindependent; whereby, the tooth spaces are engraved on an outerperiphery of rotors along a screw tooth spiral. While the working spacesare communicated with the expanded-bore-faces 03 a or 03 b, the workingspaces are gradually expanded to a maximum volume, inhaling a gasthrough a gas inlet; then, the working spaces pass through the suctionseal line (the suction containment boundary locus) 05, and the workingspaces form a closed space the boundary of which includes a male rotorside main-bore-face 02 a and a female rotor side main-bore-face 02 b.Thus, after the working space becomes a closed space, the volume of theworking spaces is gradually reduced and a confined gas within the spaceis compressed; at a last stage of compression, the gas inside the spacesis discharged through a discharge opening.

During the mentioned compression process, a liquid such as oil or wateris injected into the working space, for the purpose of cooling, sealing,and lubricating.

FIGS. 10 a and 10 b schematically depicts bore faces of a conventionalscrew rotor casing. FIG. 10 a shows a transparently perspective viewseen from the top, depicting a suction seal line and a lip part. FIG. 10b is a development of FIG. 10 a.

In FIGS. 10 a and 10 b, the reference numeral 01 a denotes a male rotorside casing, and the numeral 01 b does a femamale rotor side casing 01b; a suction seal line 05 is formed on a boundary between a male rotorside main-bore-face 02 a and the male rotor side expanded-bore-face 03 aas well as between the female rotor side main-bore-face 02 b and thefemale rotor side expanded-bore-face 03 b; a lip part 04 of the casing01 protrudes inside, toward screw rotors.

The working (operation) spaces formed with the male rotor and the femalerotor face the male rotor side expanded-bore-face 03 a and the femalerotor side expanded-bore-face 03 b, while the working spaces graduallyincrease during a suction process, inhaling a gas through a gas inlet.After the volume of the working spaces reaches a maximum volume and theworking spaces cross the suction seal line 05, the spaces form a sealedspace, being surrounded by the main-bore-faces 02 a and 02 b.Subsequently, as the volume of the working spaces is reduced, the gasconfined in the spaces is compressed. And the compressed gas isdischarged through a discharge opening at a discharge side end face 07of the rotor casing.

In the above situation, the liquid such as oil or water injected intothe working spaces leaks toward a lower pressure suction side andaccumulates in the concaved expanded bore faces 03 a/03 b. The lip part04 prevents the liquid from leaking and scattering toward the gassuction end face 06 of the rotor casing.

Patent literatures:

-   -   Patent literature 1, JP 1967-10027;    -   Patent literature 2, JP 1991-194183;    -   Patent literature 3, JP 1999-13661.

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

In spite of the disclosure according to the configuration such as in thepatent literature 3, the conventional technologies are insufficient insealing a liquid within the working spaces as well as in preventingdeterioration as to volumetric efficiency; the insufficiency is causedon the ground that great distances remain between rotor tooth tips andthe lip part 04 (04 a and 04 b in FIGS. 10 a and 10 b) placed at thesuction side end face of the rotor casings.

As just mentioned above, the lip part is provided at the suction sideend face of the rotor casings in conventional liquid injection screwcompressors; thus, a gas inlet has to be placed outside across thesuction side end face; moreover, the lip part lessens a gas inletpassage area (opening area) around the suction side end face of therotor casings; therefore, in case of manufacturing a mono-block castingof the rotor casings and the gas inlet casing, it becomes difficult toallocate a casting core for rotor casing bores.

Further, in conventional ways, only by means of lengthening rotor spacein the axial direction, it is possible to secure a sufficient gas inletpassage for inhaling a gas into the working space; in addition,insufficient inlet passage area enhances suction resistance during ahigh-speed operation.

Because of the above-mentioned situations, it is conventionallydifficult to obtain a mono-block casting of the rotor casings and thegas inlet casing. That is, in casting, it is necessary to manufacturethe rotor casing and the gas inlet casing separately; further, itbecomes necessary to provide each casing with an essentially uselesspart such as an additional flange that is needed for assembling theparts. Thus, an increased whole weight and an intricate productionprocess are brought; further, as mentioned above, in a high speedoperation, there arise difficulties such as an increased gas suctionresistance as well as a lessened volumetric efficiency.

In view of the mentioned subjects in conventional liquid injection typescrew compressors, the goals of the present invention are:

-   -   preventing a liquid such as oil or water from leaking outside        the working spaces of high compression, which are formed by        screw rotors, toward the gas inlet side during a compression        process, more effectively than conventional ways;    -   lessening a gas suction resistance of a gas flow into the rotor        casings from an outside gas inlet so as to improve volumetric        efficiency of the inhaled gas, as a result; and    -   realizing an liquid injection type screw compressors of a        simplified structure so as to bring manufacturing cost        reduction.

Further, the invention aims at realizing a liquid injection type screwcompressor provided with a variable compression ratio mechanism, thatis, an internal volume ratio adjusting valve; wherein, the compressorhas a compact structure so as to not prolong a manipulation mechanism ofthe internal volume ratio adjusting valve, making manufacturing cost befurther reduced.

Means to Solve the Problem

In order to attain the mentioned goals, the present invention proposes aliquid injection type screw compressor comprising of:

-   -   a pair of a male rotor and a female rotor,    -   a rotor casing comprising a pair of bores that accommodate the        pair of the male rotor and the female rotor,    -   a gas inlet and a gas outlet that are connected to the pair of        the bores, the gas inlet being provided at a first end part of        the rotor casing, while the gas outlet being provided at a        second end part of the rotor casing, and    -   a lip part that is provided on a surface of the bores and        protrudes inside so as to prevent the liquid on the surfaces of        bores from back-flowing toward the gas inlet, the lip part being        located at a gas upstream side of a suction seal line of the        rotor casing;    -   wherein the lip part is placed within a range between the        suction seal line and a line that is apart from the suction seal        line, by one screw pitch distance of the screw rotors, toward        the expanded-bore-face side of the male rotor side casing and/or        the female rotor side casing (namely, toward the gas inlet        side).

In a screw compressor according to the present invention, a lip part forpreventing liquid from back-flowing toward a gas inlet is provided on acasing bores, within a range between a suction seal line and a line thatis apart from the suction seal line, by one screw pitch distance of thescrew rotors, toward the expanded-bore-face side of the male rotor sidecasing and/or the female rotor side casing; hence, the lip part isplaced nearer to the suction seal line in comparison with conventionalways; as a result, a liquid leakage from the compressed working spacestoward the gas inlet side is effectively prevented; further, the lippart placed nearer to the suction seal line makes it possible toeliminate a part of bore faces that is located at the gas inlet sidefrom the lip part. So can be realized a simplified configuration ofrotor casings with a reduced bore surface as well as a reduced suctionresistance and a reduced manufacturing cost which are attributable tothe simplification.

A preferable configuration of the present invention may comprise:

-   -   a straight development-line portion of the suction seal line in        a development view, lying at right angles to a bore intersection        line that is defined as a common generating line of a male rotor        bore and a female rotor bore,    -   a lip-entering-edge of the lip part that is placed apart from        the suction seal line toward the gas inlet side in a rotor axis        direction, whereby the lip-entering-edge in response to the        above-mentioned straight-line portion is bent so as to protrudes        toward the suction seal line, and    -   a lip ending (trailing) edge of the lip part whereby the lip        ending edge in response to the straight-line portion is placed        parallel thereto so as to form a straight line portion of the        lip ending edge in a development view, and    -   a thickened (wide in the rotor axis direction) lip part in        response to the straight-line portion.

The above preferable configuration can surely prevent a liquid leakagearound a neighborhood along the bore intersection line.

According to a further preferable aspect of the above configuration,

-   -   the straight line portion of the suction seal line in a        development view lies at right angles to the bore intersection        line, and starts from a cross-point of the bore intersection and        the suction seal line on the male bore surface as far as a point        on the suction seal line on the female bore surface,    -   the lip-entering-edge of the lip part is placed apart from the        suction seal line toward the gas inlet side in the rotor axis        direction, and the lip-entering-edge in response to the        above-mentioned straight-line portion is bent so as to protrudes        toward the suction seal line; wherein, a part of the        lip-entering-edge in response to the straight line portion        starts from a cross-point of the bore intersection line and the        lip-entering-edge on the male bore surface, as far as a point on        the lip-entering-edge on the female bore surface,    -   the lip ending (trailing) edge of the lip part in response to        the straight-line portion is placed parallel thereto so as to        form the straight line portion of the lip ending edge in a        development view, and    -   the thickened (wide in the rotor axis direction) lip part is        provided in response to the straight-line portion, whereby a        straight line portion of the ending edge starts from a        cross-point of the bore intersection and the lip-ending-edge on        the male bore surface, as far as a point on the lip-ending-edge        on the female bore surface.

The above configuration can surely prevent a liquid leakage around thebore intersection line.

Another preferable aspect of the invention according to the mentionedconfiguration is the liquid injection type screw compressor, wherein therotor casing with the gas inlet casing is formed in one piece or aplurality of divided-pieces from the lip ending edge toward a gasdownstream side. Thus, the gas inlet side bore surface of the rotorcasing can be omitted in a way that the lip part is located nearer tothe suction seal line; as a result, it becomes possible to form a gasinlet casing and a rotor casing in one body.

Consequently, the invention realizes a smaller rotor casing, saving aninstallation space; in addition, the invention greatly relievesrestrictions concerning a position where a gas inlet casing is disposedin a rotor casing; in this regard, the degree of freedom as to the gasinlet casing design can be greatly expanded.

According to a further preferable aspect of the invention, a labyrinthstructure is embodied on the inner surface which faces rotor tooth tipsin the lip part. For example, a pertinent roughness of the surface (e.g. a pertinent casting surface roughness) or an intended uneven surfacecan realize lesser liquid leakage.

According to another preferable aspect of the invention, different outerdiameters are applied to a pair of the male rotor and the female rotorso that the outer diameter of the male rotor is greater than that of thefemale rotor, and the number of the male rotor teeth is fewer than thatof the male rotor teeth in a case when the same outer diameter isapplied to a pair of the male rotor and the female rotor.

In this way, a screw pitch distance of the male rotor can be shortenedand the lip part can be located nearer to the suction seal line; thus,the liquid leakage can be further surely prevented; in addition, thegeometry of the casings can be simplified.

According to another preferable aspect of the invention, the lip part isprovided at the lower side of the casing bore surfaces. In thisconfiguration, the liquid accumulated by gravity at the bottom of thebore surfaces can be easily prevented from scattering toward the gasinlet side; thus, a simple structure can be realized.

Another preferable aspect of the invention according to the mentionedconfiguration is a liquid injection type screw compressor comprising:

-   -   a slide valve (capacity control valve), and    -   an internal volume ratio (U_(i)) adjusting valve; whereby, the        slide valve has    -   a cut-out part, at a discharge end thereof, which regulates a        gas discharge throat between a discharge end part (of gas        discharge side) of the slide valve and an end face (of gas        discharge side) of the rotor casing, and    -   a valve driving rod (a pushrod) that is prolonged toward the gas        inlet casing on a rotor end face so that the valve driving rod        protrudes across the gas inlet casing, through a storage space        of the internal volume ratio adjusting valve that is provided on        a side of the gas inlet casing which comes in contact with the        rotor end face, the valve driving rod being connected to a drive        source i.e. a hydraulic cylinder in order that the slide valve        can move forward and backward along an axis of the driving rod        by means of the drive source and the driving rod,    -   while the internal volume ratio (U_(i)) adjusting valve in the        storage space is placed adjacent to a gas inlet side end face of        the capacity control valve (a slide valve), with a positioning        means that adjusts variably the position of the internal volume        ratio (U_(i)) adjusting valve, along a direction to/from a gas        discharge side,    -   wherein an internal volume ratio (U_(i)) is adjusted such that        the positioning means shifts the internal volume ratio (U_(i))        adjusting valve to a predetermined position, while an internal        gas capacity (that is equivalent to a gas density at a        compression commencement) is adjusted by by-passing an inhaled        gas back to the gas inlet side through a gap between the        internal volume ratio (U_(i)) adjusting valve, and the capacity        control valve (a slide valve) that slides to and fro along the        driving rod direction by means of the drive source, through the        driving rod.

The installation of an internal volume ratio (U_(i)) adjusting valvemakes a whole compressor compact, realizing a compressor of three kindsof compression ratios, namely, of lower/medium/higher compressionratios, without changing a gas inlet casing, only by replacing a rotorcasing. Thus, a gas inlet casing can be applied to these kinds ofcompressors in common.

On the other hand, conventional compressors are apt to be of a largesize, as a positioning means to position the internal volume ratio(U_(i)) adjusting valve is prolonged toward a gas discharge side,penetrating a gas discharging casing so as to be used for setting(positioning) the valve.

In order to solve the difficulty, according to a further preferableaspect of the present invention, the positioning means comprises:

-   -   a hollow shaft which is placed concentric to the driving rod,        having a screw part on an outer surface of the hollow shaft so        that the screw part is engaged into a corresponding screw part        inside the internal volume ratio adjusting valve, and    -   a rotation rod that is placed so as to intersect with the hollow        shaft in order that the rod can transmit a rotational driving        movement of the rod to the hollow shaft, via a connection part;        whereby, the rotational movement transmitted to the hollow shaft        is transformed into a to-and-fro movement of the internal volume        ratio adjusting valve, through the mentioned screw engagement,        so that the internal volume ratio adjusting valve is positioned        to a predetermined position.

According to the above aspect, there is no need to prolong a positioningmeans as in conventional approaches; a driving mechanism to position theinternal volume ratio-adjusting valve can be formed as a compact one.The mentioned connection part between the hollow shaft and the rotationrod may be a bevel gear pair or a crossed helical gear pair.

Effect of the Invention

In a screw compressor according to the disclosed invention, a lip partfor preventing liquid from back-flowing toward a suction inlet isprovided on a casing bores, within a range between a suction seal lineand a line that is apart from the suction seal line, by one screw pitchdistance of the screw rotors, toward the expanded-bore-face side of themale rotor side casing and/or the female rotor side casing.

Therefore, a liquid leakage scattering during a compression process fromthe compressed working space formed by the screw rotors toward the gasinlet side can be effectively prevented.

Moreover, the lip part placed nearer to the suction seal line makes itpossible to eliminate a part of the rotor casing at the gas inlet sidefrom the lip part. So can be realized a simplified configuration ofrotor casings with a reduced bore surface as well as a reduced suctionresistance of an inhaled gas and an enhanced volumetric efficiency ofthe compressor.

Further, the lip part placed nearer to the suction seal line makes itpossible to eliminate a part of the rotor bore faces at the gas inletside from the lip part. Hence, the rotor casing can be formed in onebody with a gas inlet casing. As a result, manufacturing processes canbe simplified and a manufacturing cost can be reduced. Consequently, thedisclosed invention greatly relieves restrictions regarding installationposition of a gas inlet casing in a rotor casing. Further, the degree offreedom as to the gas inlet casing design can be greatly expanded; inaddition, a compact casing can be realized and a compressor installationspace can be reduced.

Also as already explained, in a screw compressor according to thedisclosed invention, the compressor comprises:

-   -   a straight development-line portion of the suction seal line in        a development view, lying at right angles to a bore intersection        line that is defined as a common generating line of a male rotor        bore and a female rotor bore,    -   a lip-entering-edge of the lip part that is placed apart from        the suction seal line toward the gas inlet side in a rotor axis        direction, whereby the lip-entering-edge in response to the        above-mentioned straight-line portion is bent so as to protrudes        toward the suction seal line, and    -   a lip ending (trailing) edge of the lip part whereby the lip        ending edge in response to the straight-line portion is placed        parallel thereto so as to form a straight line portion of the        lip ending edge in a development view, and    -   a thickened (wide in the rotor axis direction) lip part in        response to the straight-line portion.

Thus, the above configuration can surely prevent a liquid leakage arounda neighborhood along the bore intersection line.

Further, in a screw compressor according to the disclosed invention, thecompressor comprises:

-   -   the straight line portion of the suction seal line in a        development view lies at right angles to the bore intersection        line, and starts from a cross-point of the bore intersection and        the suction seal line on the male bore surface, as far as a        point on the suction seal line on the female bore surface,    -   the lip-entering-edge of the lip part is placed apart from the        suction seal line toward the gas inlet side in the rotor axis        direction, and the lip-entering-edge in response to the        above-mentioned straight-line portion is bent so as to protrudes        toward the suction seal line; wherein, a part of the        lip-entering-edge in response to the straight line portion        starts from a cross-point of the bore intersection and the        lip-entering-edge on the male bore surface, as far as a point on        the lip-entering-edge on the female bore surface,    -   the lip ending (trailing) edge of the lip part in response to        the straight-line portion is placed parallel thereto so as to        form the straight line portion of the lip ending edge in a        development, and    -   the thickened (wide in the rotor axis direction) lip part is        provided in response to the straight-line portion, whereby a        straight line portion of the ending edge starts from a        cross-point of the bore intersection and the lip-ending-edge on        the male bore surface, as far as a point on the lip-ending-edge        on the female bore surface.

Thus, the above configuration can surely prevent a liquid leakage arounda neighborhood along the bore intersection line.

Further, in a screw compressor according to the disclosed invention,different outer diameters are applied to a pair of the male rotor andthe female rotor so that the outer diameter of the male rotor is greaterthan that of the female rotor, and the number of the male rotor teeth isfewer than that of the male rotor teeth in a case when the same outerdiameter is applied to a pair of the male rotor and the female rotor.

In this manner, a screw pitch distance of the male rotor can beshortened and the lip part can be located nearer to the suction sealline; thus, the liquid leakage can be further surely prevented; inaddition, the geometry of the casings can be simplified.

Further, in a screw compressor according to the disclosed invention, thecompressor comprises:

-   -   a slide valve (capacity control valve), and    -   an internal volume ratio (U_(i)) adjusting valve; whereby, the        slide valve has    -   a slide valve (capacity control valve), and an internal volume        ratio (U_(i)) adjusting valve; whereby, the slide valve has    -   a cut-out part, at a discharge end thereof, which regulates a        gas discharge throat between a discharge end part (of gas        discharge side) of the slide valve and an end face (of gas        discharge side) of the rotor casing, and    -   a valve driving rod (a pushrod) that is prolonged toward the gas        inlet casing on a rotor end face so that the valve driving rod        protrudes across the gas inlet casing, through a storage space        of the internal volume ratio adjusting valve that is provided on        a side of the gas inlet casing which comes in contact with the        rotor end face, the valve driving rod being connected to a drive        source in order that the slide valve can move forward and        backward along an axis of the driving rod by means of the drive        source and the driving rod,    -   whereas the internal volume ratio adjusting valve in the storage        space is placed adjacent to a gas inlet side end face of the        capacity control valve (a slide valve), with a positioning means        that adjusts variably the position of the internal volume ratio        adjusting valve, along a direction to/from a gas discharge side,    -   wherein an internal volume ratio is adjusted such that the        positioning means shifts the internal volume ratio adjusting        valve to a predetermined position, while an internal gas        capacity is adjusted by by-passing an inhaled gas back to the        gas inlet side through a gap between the internal volume ratio        adjusting valve, and the capacity control valve (a slide valve)        that slides to and fro along the driving rod direction by means        of the drive source, through the driving rod.

According to the above disclosure, the installation of an internalvolume ratio (U_(i)) adjusting valve can make a whole compressorcompact, realizing a compressor of three kinds of compression ratios,namely, of lower/medium/higher compression ratios, without changing agas inlet casing, only by replacing a rotor casing. Thus, a gas inletcasing can be applied to these kinds of compressors in common.

Still further, in a screw compressor according to the disclosedinvention, the compressor comprises a positioning means for positioningthe internal volume ratio-adjusting valve, the positioning meanscomprising:

-   -   a hollow shaft which is placed concentric to the driving rod,        having a screw part on an outer surface of the hollow shaft so        that the screw part is engaged into a corresponding screw part        inside the internal volume ratio adjusting valve, and    -   a rotation rod that is placed so as to intersect with the hollow        shaft in order that the rod can transmit a rotational driving        movement of the rod to the hollow shaft, via a connection part;        whereby, the rotational movement transmitted to the hollow shaft        is transformed into a to-and-fro movement of the internal volume        ratio adjusting valve, through the mentioned screw engagement,        so that the internal volume ratio adjusting valve is positioned        to a predetermined position.

According to the above aspect, there is no need to prolong a positioningmeans as in conventional approaches; a driving mechanism to position theinternal volume ratio-adjusting valve can be formed as a compact one.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in greater detail withreference to the preferred embodiments of the invention and theaccompanying drawings, wherein:

FIG. 1 a shows a transparently perspective view seen from a top as to afirst embodiment of the present invention;

FIG. 1 b is a development view of FIG. 1 a;

FIG. 2 a shows a perspective view of an upper side rotor-casing seenfrom the inside thereof, as to a first embodiment;

FIG. 2 b shows a perspective view of a lower side rotor-casing seen fromthe inside thereof, as to the first embodiment;

FIG. 3 shows a perspective view of apart of a rotor casing as to thefirst embodiment;

FIG. 4 shows a longitudinal plan view of a second embodiment of thepresent invention;

FIG. 5 shows a longitudinal section view concerning the secondembodiment;

FIG. 6 explains a development view showing a suction seal line (asuction containment boundary locus) as to each of the male/female rotorsthat have different tip diameters;

FIG. 7 gives an explanation about the male/female rotors that havedifferent tip diameters;

FIG. 8 shows a perspective view as to a variation of the secondembodiment;

FIG. 9 a shows a perspective view of an upper side rotor-casing seenfrom the inside thereof, as to a conventional compressor;

FIG. 9 b shows a perspective view of a lower side rotor-casing seen fromthe inside thereof, as to a conventional compressor;

FIG. 10 a shows a transparently perspective view seen from the top as toa conventional compressor in consideration of a schematic explanationfor bore faces thereof; and

FIG. 10 b is a development view of FIG. 10 a.

REFERENCE NUMERALS

-   01 a, 1 a, and 11 a a male rotor side casing;-   01 b, 1 b, and 11 b a female rotor side casing;-   02 a and 2 a a male rotor side main-bore-face;-   02 b and 2 b a female rotor side main-bore-face;-   03 a and 3 a a male rotor side expanded-bore-face;-   03 b and 3 b a female rotor side expanded-bore-face;-   04, 4, and 33 a lip part;-   4 c and 33 c a thickened lip part;-   4 d and 33 d a lip entering edge;-   4 e and 33 e a lip ending (trailing) edge-   05, 5, and 32 a suction seal line (a suction containment boundary    locus)-   5 c and 32 c a straight line portion of a suction seal line in a    development view-   06 and 6 a suction side end face-   07 and 7 a discharge side end face-   08, 8, and 34 a bore intersection line (that is defined-   as a common generating line of a male rotor bore and a female rotor    bore)-   9 and 12 a gas inlet (a suction inlet)-   11 a rotor casing-   13 a gas inlet casing-   14 a male rotor shaft-   15 a female rotor shaft-   16 and 19 a thrust bearing-   17, 18, 20, and 21 a radial bearing (a journal bearing)-   22 a male rotor-   23 a female rotor-   24 a mechanical seal-   25 a discharge outlet (a gas outlet)-   26 a gas outlet casing-   27 and 36 a tightening bolt-   28 a slide valve (a capacity control valve)-   28 a a cut-out part-   29 a pushrod (a valve driving rod for manipulating a capacity    control valve)-   30 an oil-hydraulic cylinder (for driving a capacity    /displacement-volume control valve)-   31 an internal volume ratio (U_(i)) control device of a manual    operation type-   35 a casing-   37 an internal volume ratio (U_(i)) adjusting valve for adjusting    compression ratio U_(i)-   38 a hollow shaft-   39 a and 39 b a bevel gear (a movement communicating part)-   40 a rotation-rod-   41 a discharge opening-   “a” in FIG. 4 an intersection point of a suction seal line and a    bore intersection line-   “b” in FIG. 4 an intersection point of a lip entering edge and a    bore intersection line-   “c” in FIG. 4 an intersection point of a lip ending (trailing) edge    and a bore intersection line

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, the present invention will be described in detail withreference to the embodiments shown in the figures. However, thedimensions, materials, shape, the relative placement and so on of acomponent described in these embodiments shall not be construed aslimiting the scope of the invention thereto, unless especially specificmention is placed.

FIG. 1 a shows a transparently perspective view seen from the top as toa first embodiment of the present invention; FIG. 1 b is a developmentview of FIG. 1 a; FIG. 2 a shows a perspective view of an upper siderotor-casing seen from the inside thereof, as to the first embodiment;FIG. 2 b shows a perspective view of a lower side rotor-casing seen fromthe inside thereof, as to the first embodiment; FIG. 3 shows aperspective view of a part of a rotor casing as to the first embodiment;FIG. 4 shows a longitudinal plan view of a second embodiment of thepresent invention; FIG. 5 shows a longitudinal section view concerningthe second embodiment; FIG. 6 explains a suction seal line (a suctioncontainment boundary locus) as to each of the male/female rotors thathave different tip diameters; FIG. 7 gives an explanation about themale/female rotors that have different tip diameters; FIG. 8 shows aperspective view as to a variation of the second embodiment;

FIRST EMBODIMENT

FIGS. 1 a and 1 b schematically depict a bore face in a rotor casing ofa screw compressor according to the present invention; FIG. 1 a shows aperspective view as to a suction seal line (a suction containmentboundary locus) and a lip part on the bore face seen transparently froma top; and, FIG. 1 b is a development view of FIG. 1 a; in FIGS. 2 a and2 b, the rotor-casing is divided into an upper side part and a lowerside part so that the bore face of the casing is easily explained.

In a male rotor side casing la and a female rotor side casing 1 b ofFIGS. 1 a, 1 b, 2 a, 2 b, and 3, a suction seal line (a suctioncontainment boundary locus) 5 is formed on a boundary between main borefaces 2 a/2 b and expanded bore faces 3 a/3 b, whereby the main borefaces 2 a/2 b are located opposite to addendum circles of the a malerotor and a female rotor, with a slight clearance, while a lip part 4 asa protruding part is provided apart from the suction seal line 5, by ascrew pitch distance to a suction side end face 6. Here, an example ofdimension data is such that a clearance between the main bore faces 2a/2 b and the addendum circles of the a male rotor and a female rotor issubstantially 0.05 mm to 0.125 mm (a clearance to a diameter c/D=0.8 to1.0/1000), while a distance between the expanded bore faces 3 a/3 b andthe addendum circles of the rotors is substantially 5 mm (a clearance toa diameter c/D=0.05 to 0.06). It is noted hereby that c and d denote aclearance and a diameter respectively.

The suction seal line 5 includes a curved part 5 a that is on a mainbore face of the male rotor side casing 1 a, a curved part 5 b that ison a main bore face of the female rotor side casing 1 b, and a curvedpart 5 c that is also on the main bore face of the female rotor sidecasing 1 b; whereby, in the development figures of FIGS. 1 a and 1 b,the curved part 5 c is seen as a straight line which starts from a point“a” that is a cross point of the curved part 5 a and a bore intersectionline 8; further, in FIGS. 1 a and 1 b, the straight line lies at rightangles to the bore intersection line 8, while the straight line ends apoint where the line intersects with the curved part 5 b.

On the other hand, in response to the suction seal line 5, the geometryof the lip part 4 comprises:

-   -   a lip-entering-edge 4 d of the lip part 4 c that is placed apart        from the suction seal line, within one screw pitch distance,        toward the gas inlet side along a rotor axis direction, whereby        the lip-entering-edge in response to the above-mentioned        straight-line 5 c is bent so as to protrudes toward the suction        seal line; wherein, a part of the lip-entering-edge in response        to the straight line portion starts from a cross-point “b” of        the bore intersection line 8 and the lip-entering-edge on the        male bore surface, as far as a point on the lip-entering-edge on        the female bore surface,    -   a lip ending (trailing) edge 4 e of the lip part 4 c whereby the        lip ending edge in response to the straight-line 5 c is placed        parallel thereto so as to form a straight line portion of the        lip ending edge in a development view; wherein, a straight line        portion of the ending edge starts from a cross-point “c” of the        bore intersection line 8 and the lip-ending-edge on the male        bore surface, as far as a point on the lip-ending-edge on the        female bore surface, and    -   a thickened (wide in the rotor axis direction) lip part 4 c in        response to the straight-line portion 5 c.

Liquid such as oil or water injected into a compression working space isapt to leak toward a lower pressure suction side and accumulates inconcaved expanded bore faces 3 a/3 b. The lip part 4 prevents the liquidfrom leaking and scattering toward a gas inlet side.

According to the first embodiment as described above, the distancebetween the suction seal line 5 and the lip part 4 is substantiallywithin one screw pitch distance; thus, the lip part 4 is provided at alocation closer to the suction seal line 5 in comparison withconventional ways. Therefore, in comparison with conventional ways, iseffectively prevented a liquid leakage that scatters, during acompression process, from the compressed working space which is formedby the screw rotors toward the gas inlet side. Moreover, the lip partplaced nearer to the suction seal line makes it possible to eliminate apart of the rotor casing, located at the gas inlet side from the lippart. So can be realized a simplified configuration of rotor casingswith a reduced bore surface as well as a reduced suction resistance ofan inhaled gas and an enhanced volumetric efficiency of the compressor.

Further, in the above embodiment, a straight line portion 5 c of thesuction seal line 5 is provided in the neighborhood of the boreintersection line, the line lying at right angles with the boreintersection line in a development view. In addition, a thickened lippart 4 c is provided, comprising:

-   -   a lip-entering-edge 4 d of the lip part 4 c that is placed apart        from the suction seal line, within one screw pitch distance,        toward the gas inlet side in a rotor axis direction, wherein the        lip-entering-edge in response to the above-mentioned        straight-line portion 5 c is bent so as to protrudes toward the        suction seal line; and    -   a lip ending (trailing) edge 4 e of the lip part 4 c, being        placed parallel to the straight line portion 5 c so as to form a        straight line portion of the lip ending edge in a development        view; wherein, the straight line portion of the ending edge is        vertical to the bore intersection line 8 in a development.

In this manner, can be surely prevented a liquid leakage around theneighborhood along the bore intersection line, toward a gas inlet side,from the working (compression) spaces which are formed by the malefemale rotors.

Moreover, it becomes possible to eliminate a part from the lip part 4toward a side of the gas inlet 9 in the rotor casing; in addition, asimplified configuration of rotor casings can be realized. Further,since the gas inlet casing can be placed nearer to the rotor casing, therotor casing can be formed in one body together with the gas inletcasing. As a result, manufacturing processes can be simplified and amanufacturing cost can be reduced.

SECOND EMBODIMENT

A second embodiment of the present invention is now detailed withreference to FIGS. 4 to 8. As shown in FIG. 7, in the second embodimenta male rotor and a female rotor of different rotor sizes, namelydifferent outer diameters, are used; where the outer diameter of themale rotor is larger than that of the female rotor, and the number ofteeth as to the male rotor is 5, while that as to the female rotor is 6.

In FIGS. 4 and 5, the reference numeral 11 denotes the rotor casing thataccommodates both the male rotor and the female rotor, and the rotorcasing 11 together with a gas inlet casing 13 that forms a gas inlet 12is made of mono casting. The rotor casing 11 accommodates the male rotor22 and the female rotor 23 shown in FIG. 7, here the detail of therotors is omitted. The reference numeral 14 denotes a male rotor shaftthat is supported by a thrust bearing 16 and radial bearings 17/18,while the numeral 15 denotes a female rotor shaft that is supported by athrust bearing 19 and radial bearings 20/21.

A mechanical seal 24 is provided near a shaft end part 14 a of the malerotor shaft 14, the shaft end part 14 a being connected to an outputshaft of a drive motor (not shown) as a power source.

A gas outlet casing 26 that forms a gas outlet 25 is made of casting;however, the casing 26 is made of different casting from the rotorcasing 11, and the casing 26 is fastened thereto with tightening bolts27. At a lower part of the rotor casing 11, is provided a slide valve (acapacity control valve) 28 that makes it possible to regulate acompressor capacity (an inhaled gas capacity) by means ofsliding-manipulation along an axis direction of the rotors; thereby, apushrod (a driving rod) 29 regulates a length as to thesliding-manipulation of the slide valve 28. In addition, the pushrod 29is operated through an oil pressure that is supplied to a left cylinderroom 30 a and a right cylinder room 30 b in an oil-hydraulic cylinder30.

At the middle part of the pushrod 29, is installed a U_(i)-controldevice (an internal volume ratio control device) 31 of a manualoperation type; hereupon, the device 31 makes it possible to optimizethe internal volume ratio U_(i). A casing 35 that contains theU_(i)-control device 31 is fastened to the gas inlet casing 13 withtightening bolts 36, while the oil-hydraulic cylinder 30 is fitted tothe casing 35. The reference numeral 37 denotes an internal volume ratio(U_(i)) adjusting valve; thereby, the U_(i)-adjusting valve 37 isengaged into a screw part 38 a that is provided on an outer face of ahollow shaft 38. Here, the hollow shaft 38 is installed around thepushrod 29 having a round cross-section, so that a round hollow cylinderof the hollow shaft 38 and the round cross-section of the pushrod 29 areconcentric, and the hollow shaft 38 can rotate freely around the pushrod29. Further, the U_(i)-adjusting valve 37 moves along the rotor axeswith a rotational movement of the hollow shaft 38.

On the other hand, the reference numeral 39 a denotes a bevel gear thatis fitted to a suction-side end part of the hollow shaft 38, while thebevel gear 39 a is engaged in a corresponding bevel gear 39 b that isfitted to an end part of a rotation-rod 40; hereupon, it is noted thatthe axes of the hollow shaft 38 and the rotation-rod 40 lie at rightangles to each other.

According to the above-mentioned configuration, when the rotation-rod 40is rotated, either clockwise or counterclockwise, a rotational movementis transmitted to the hollow shaft 38; as a result, the U_(i)-adjustingvalve 37 moves back and forth along an rotor axis, through an engagementof the screw part 38 a and the U_(i)-adjusting valve 37. A steeringwheel (not shown) or the like may be fitted to the rotation-rod 40 so asto enable an operator to turn the wheel by hand in case of manualcontrol.

When the internal volume ratio (U_(i)) is adjusted, the followingsequence of manipulations is performed: rotating the rotation-rod 40under a stop condition of the compressor; making the U_(i)-adjustingvalve 37 move along an rotor axis; as a result, thrusting the slidevalve 28 toward the gas outlet 25; adjusting an opening level of adischarge opening 41 that is formed between a cut-out part 28 a providedat a discharge-front end side of the slide valve 28, and the gas outletcasing 26; thus, initializing the internal volume ratio (U_(i)).

In addition, when a capacity of the compressor needs to be adjusted, theslide valve 28 is shifted along the axes of the rotors through amovement of the pushrod 29; thereby, a by-passed gas flow toward the gasinlet side from a gap between the slide valve 28 and the pushrod 29controls the capacity (the inhaled gas flow quantity).

FIG. 6 shows the male rotor 22, the female rotor 23, and the suctionseal line 32 in the second embodiment, in which the male rotor 22 andthe female rotor 23 of different rotor sizes, namely, different outerdiameters, are used, where the outer diameter of the male rotor islarger than that of the female rotor; in addition, the number of teethas to the male rotor is 5, while the number of teeth spaces as to thefemale rotor is 6.

Incidentally, in FIG. 4, are shown the suction seal line 32 and the lippart 33, for explanation use. Similar to FIG. 1 as to the firstembodiment, the lip part 33 is provided apart from the suction seal line5, by a screw pitch distance, toward the gas inlet side.

As shown in FIGS. 4 and 6, the suction seal line 32 comprises:

-   -   a curved part 32 a on the bore in the male rotor casing 11 a,    -   a curved part 32 b on the bore in the female rotor casing 11 b,        and    -   a straight line portion 32 c in a development view whereby the        straight part lies at right angles to the bore intersection line        34; wherein, the straight line starts from a cross-point “a” of        the bore intersection line 34 and the curved part 32 a, as far        as a point on the curved part 32 b on the bore in the female        rotor casing 11 b.

Further, the lip part 33 comprises a male casing side lip part 33 a onthe bore in the male rotor casing 11 a, and a female casing side lippart 33 b, while the boundary of the lip part 33 comprises alip-entering-edge and a lip ending (trailing) edge; hereupon, the lippart 33 is away from the suction seal line, within a screw pitchdistance.

Still further, the lip-ending-edge comprises:

-   -   a straight line portion 33 e, in response to the straight line        32 c of the suction seal line 32, and lying at right angles to        the bore intersection line 34 in a development view, while the        line portion 33 e starts a cross-point “c” of the bore        intersection line 8 and the lip-ending-edge on the bore in the        male rotor casing 11 a, as far as a point of the lip-ending-edge        on the bore in the female rotor casing 11 b; in addition,    -   the lip-entering-edge comprises:    -   a bent curve portion 33 d, in response to the straight line        portion 32 c of the suction seal line 32, whereby the bent curve        portion 33 d protrudes toward the straight line portion 32 c of        the suction seal line 32, while the bent curve portion 33 d        starts a cross-point “b” of the bore intersection line 8 and the        lip-entering-edge on the bore in the male rotor casing 11 a, as        far as a point of the lip-entering-edge on the bore in the        female rotor casing 11 b.

In the above-mentioned manner, a thickened lip part 33 c is formed withthe bent curve portion 33 d and the line portion 33 e, in response tothe straight line portion 32 c of the suction seal line 32. So can besurely prevented a liquid leakage around the neighborhood along the boreintersection line, toward a gas inlet side, from the working(compression) spaces in the rotor casing 11.

According to the second embodiment, in the same way as the firstembodiment, the lip part 33 is provided apart from the suction seal line5, by a screw pitch distance, toward the gas inlet side; thus, can besurely prevented a liquid leakage around the neighborhood along the boreintersection line, toward a gas inlet side, from the working(compression) spaces. Further, since the lip part is provided around theneighborhood along the bore intersection line as mentioned above, aliquid leakage around the bore intersection line can be surelyprevented.

Moreover, can be eliminated a part of the rotor casing on the gas inletside of the lip part 33. Thus, can be secured a satisfactory space thatcommunicates the bore faces of the rotor casing to the gas inlet 12, thespace reducing a suction resistance of the gas inhaled from the gasinlet 12. As a result, a volumetric efficiency of the compressor can beenhanced.

On the other hand, by means of eliminating a part of the rotor casingthe part which is located on the gas inlet side of the lip part, thelocation of the gas inlet 12 can be shifted toward the rotor casing 11.Thus, the rotor casing 11 together with a gas inlet casing 13 that formsa gas inlet 12 can be made of mono casting. In this way, a compactcasing can be realized and a compressor installation space can bereduced. Consequently, a compact casing can be realized, a compressorinstallation space can be reduced, a compressor manufacturing cost canbe greatly lowered, and the degree of freedom as to the gas inlet casingdesign about the rotor axis direction can be expanded.

Further, it becomes possible to design a compressor casing of the samekind compressors so that a distance L between an axis “i” of the gasinlet 12 and an axis “o” of the gas outlet 25 can be kept constant.Therefore, a manufacturing line of the compressor casings can bestreamlined so as to mechanized and robotized.

The installation of an internal volume ratio (U_(i)) adjusting valvemakes a whole compressor compact, realizing a compressor with threekinds of compression ratios , namely, of lower/medium/higher compressionratios, without changing sorts of a gas inlet casing, only by replacinga rotor casing. Thus, a gas inlet casing can be applied to these kindsof compressors in common. Namely, even if the rotor-casing is replacedby another one for constituting a different kind (capacity) of thecompressor, it is not necessary to exchange the gas inlet casing.

Further, conventional compressors are apt to be of a large size, as apositioning means to position the internal volume ratio (U_(i))adjusting valve is prolonged toward a gas discharge side, penetrating agas outlet casing so as to be used for positioning the valve. Contraryto the above, the second embodiment comprises a positioning means forpositioning the internal volume ratio-adjusting valve including:

a hollow shaft 38 , and

-   -   a rotation rod 40 that is placed so as to intersect with the        hollow shaft with right angles in order that the rod can        transmit a rotational driving movement of the rod to the hollow        shaft, via a bevel gear pair 39 a/39 b.

According to the above configuration, there is no need to prolong apositioning means as in conventional approaches; a driving mechanism toposition the internal volume ratio-adjusting valve 37 can be formed as acompact one.

Incidentally, for the connection part between the rotation rod 40 andthe hollow shaft 38, a crossed helical gear pair may be applied insteadof a bevel gear pair; a bevel gear pair tends to have a play to someextent between meeting gears, while a crossed helical gear has littleplay.

INDUSTRIAL APPLICABILITY

According to the present invention regarding a liquid injection typescrew compressor, a liquid leakage, such as an oil leakage or a waterleakage, that flows back to a gas inlet side from a compression roomwhich is formed screw rotors is further effectively prevented incomparison with conventional compressors of the same kind. In addition,suction resistance of the gas inhaled from the gas inlet can be lowered,and volumetric efficiency as to the inhaled gas can be improved;further, cast modeling of a rotor casing can be simplified and amanufacturing cost can be reduced.

Thus, the invention greatly contributes to a practical compressorindustry.

This is a continuation of International Application PCT/JP2005/0020041(published as WO 2007-0542322) having an international filing date ofOct. 31, 2005. The disclosure of the priority application, in itsentirety, including the drawings, claims, and the specification thereof,is incorporated herein by reference.

1. A liquid injection type screw compressor, comprising: a pair of malerotor and female rotor, a rotor casing comprising a pair of bores thataccommodate the pair of male rotor and female rotor, a gas inlet and agas outlet that are connected to the pair of the bores, the gas inletbeing provided at a first end part of the rotor casing, while the gasoutlet being provided at a second end part of the rotor casing, and alip part that is provided on a surface of the bores and protrude insideso as to prevent the liquid on the surfaces of bores from back-flowingtoward the gas inlet, the lip part being located at a gas upstream sideof a suction seal line of the rotor casing; wherein the lip part isplaced in a range between the suction seal line and a line that is apartfrom the suction seal line within one screw pitch distance of the screwrotors.
 2. The liquid injection type screw compressor according to claim1, whereby surfaces of the bores comprise a main bore face that comes incontact with rotor tooth tips with a slight fit tolerance, and anexpanded bore face that faces rotor tooth tips with a clearance largerthan the fit tolerance, during at least a gas suction process out ofwhole working processes; wherein the suction seal line exists betweenthe main bore face and the expanded bore face.
 3. The liquid injectiontype screw compressor according to claim 1, the compressor furthercomprising: a straight development-line portion of the suction seal linein a development view, lying at right angles to a bore intersection linethat is defined as a common generating line of a male rotor bore and afemale rotor bore, a lip-entering-edge of the lip part that is placedapart from the suction seal line toward the gas inlet side in a rotoraxis direction, whereby the lip-entering-edge in response to theabove-mentioned straight-line portion is bent so as to protrudes towardthe suction seal line, and a lip ending (trailing) edge of the lip partwhereby the lip ending edge in response to the straight-line portion isplaced parallel thereto so as to form a straight line portion of the lipending edge in a development view, and a thickened (wide in the rotoraxis direction) lip part in response to the straight-line portion. 4.The liquid injection type screw compressor according to claim 3, whereinthe straight line portion of the suction seal line in a development viewlies at right angles to the bore intersection line, and starts from across-point of the bore intersection and the suction seal line on themale bore surface as far as a point on the suction seal line on thefemale bore surface, the lip-entering-edge of the lip part is placedapart from the suction seal line toward the gas inlet side in the rotoraxis direction, and the lip-entering-edge in response to theabove-mentioned straight line portion is bent so as to protrudes towardthe suction seal line; wherein, a part of the lip-entering-edge inresponse to the straight line portion starts from a cross-point of thebore intersection line and the lip-entering-edge on the male boresurface, as far as a point on the lip-entering-edge on the female boresurface, the lip ending (trailing) edge of the lip part in response tothe straight-line portion is placed parallel thereto so as to form thestraight line portion of the lip ending edge in a development view;wherein a straight line portion of the ending edge starts from across-point of the bore intersection line and the lip-ending-edge on themale bore surface, as far as a point on the lip-ending-edge on thefemale bore surface, and the thickened (wide in the rotor axisdirection) lip part in response to the straight-line portion isprovided.
 5. The liquid injection type screw compressor according toclaim 1, wherein the rotor casing with the gas inlet casing is formed inone piece or a plurality of divided-pieces from the lip ending edgetoward a gas downstream side.
 6. The liquid injection type screwcompressor according to claim 1, wherein a labyrinth structure isembodied on the inner surface which faces rotor tooth tips in the lippart.
 7. The liquid injection type screw compressor according to claim1, wherein different outer diameters are applied to a pair of the malerotor and the female rotor so that the outer diameter of the male rotoris greater than that of the female rotor, and the number of the malerotor teeth is fewer than that of the male rotor teeth in a case whenthe same outer diameter is applied to a pair of the male rotor and thefemale rotor.
 8. The liquid injection type screw compressor according toclaim 1, wherein the lip part is provided at the lower side of thecasing bore surfaces.
 9. The liquid injection type screw compressoraccording to claim 1, the compressor further comprising: a slide valve(capacity control valve), and an internal volume ratio (U_(i)) adjustingvalve; whereby, the slide valve has a cut-out part, at a discharge endthereof, which regulates a gas discharge throat between a discharge endpart (of gas discharge side) of the slide valve and an end face (of gasdischarge side) of the rotor casing, and a valve driving rod (a pushrod)that is prolonged toward the gas inlet casing on a rotor end face sothat the valve driving rod protrudes across the gas inlet casing,through a storage space of the internal volume ratio adjusting valvethat is provided on a side of the gas inlet casing which comes incontact with the rotor end face, the valve driving rod being connectedto a drive source in order that the slide valve can move forward andbackward along an axis of the driving rod by means of the drive sourceand the driving rod, whereas the internal volume ratio adjusting valvein the storage space is placed adjacent to a gas inlet side end face ofthe capacity control valve (a slide valve), with a positioning meansthat adjusts variably the position of the internal volume ratioadjusting valve, along a direction to/from a gas discharge side, whereinan internal volume ratio is adjusted such that the positioning meansshifts the internal volume ratio adjusting valve to a predeterminedposition, while an internal gas capacity is adjusted by by-passing aninhaled gas back to the gas inlet side through a gap between theinternal volume ratio adjusting valve, and the capacity control valve (aslide valve) that slides to and fro along the driving rod direction bymeans of the drive source, through the driving rod.
 10. The liquidinjection type screw compressor according to claim 9, wherein thepositioning means comprises: a hollow shaft which is placed concentricto the driving rod, having a screw part on an outer surface of thehollow shaft so that the screw part is engaged into a correspondingscrew part inside the internal volume ratio adjusting valve, and arotation rod that is placed so as to intersect with the hollow shaft inorder that the rod can transmit a rotational driving movement of the rodto the hollow shaft, via a connection part; whereby, the rotationalmovement transmitted to the hollow shaft is transformed into ato-and-fro movement of the internal volume ratio adjusting valve,through the mentioned screw engagement, so that the internal volumeratio adjusting valve is positioned to a predetermined position.
 11. Theliquid injection type screw compressor according to claim 10, wherebythe connection part between the hollow shaft and the rotation rod isformed with a bevel gear pair or a crossed helical gear pair.